Noise reducing device, manufacturing method for the noise reducing device, and pneumatic tire having the noise reducing device

ABSTRACT

Provided are: a noise reduction device with an improved adhesion of objects formed of a porous material and with a reduced processing time; a method of manufacturing the noise reduction device; and a pneumatic tire including the noise reduction device. The noise reduction device of the present invention includes: objects formed of a porous material; a band member for attaching the objects to the inner surface of a tire at two positions spaced at substantially equal intervals in the tire circumferential direction; and locking members formed of a thermoplastic resin. The band member is formed of a thermoplastic resin. Each object is disposed at a predetermined position in the tire circumferential direction, between the band member and the corresponding locking members. The locking members are bonded to the band member through the objects by thermal fusion.

This is a divisional of application Ser. No. 11/919,184, filed Oct. 12, 2009.

TECHNICAL FIELD

The present invention relates to a device for reducing cavity resonance sound generated in a pneumatic tire. Specifically, the present invention relates to a noise reduction device with an improved adhesion of objects formed of a porous material and with a reduced processing time, to a method of manufacturing the noise reduction device, and to a pneumatic tire including the noise reduction device.

BACKGROUND ART

One of causes of noise generated in pneumatic tires is cavity resonance sound associated with vibration of the air filled inside a tire. When a tire is rolled, the air inside the tire is vibrated by the vibration of the tread portion due to irregularities of a road surface, which generates this cavity resonance sound.

As means for reducing noise due to the cavity resonance phenomenon, it has been proposed to reduce time during which the air resonates at a single frequency by changing the cross-sectional area of a cavity portion formed between a tire and a rim of a wheel in accordance with a position in the tire circumferential direction (for example, refer to Patent Document 1). Moreover, for achieving a change in the cross-sectional area of the cavity portion, it has been proposed to attach a plurality of objects to the inner surface of a tread portion with a ring-shaped band member (for example, refer to Patent Document 2). By employing such methods, it is possible to easily attach objects providing a change in the cross-sectional area to the inner surface of a tire.

However, when objects formed of, for example, a porous material, such as polyurethane foam, are fixed to a band member by using an adhesive agent or an adhesive tape, the porous material sometimes reacts with a component included in the adhesive agent or the adhesive tape to be decomposed. As a result, the adhesion of the objects is deteriorated. For this reason, the means for fixing the objects to the band member has an advantage that the means facilitates the attachment of the objects to the inner surface of the tire, but is insufficient in terms of the durability. Moreover, the bonding of the objects formed of a porous material to the band member with the adhesive agent has a disadvantage that it takes a long time for the adhesive agent to set.

-   Patent Document 1: Japanese patent application Kokai publication No.     2001-113902 -   Patent Document 2: Japanese patent application Kokai publication No.     2003-226104

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a noise reduction device with an improved adhesion of objects formed of a porous material and with a reduced processing time, a method of manufacturing the noise reduction device, and a pneumatic tire including the noise reduction device.

A noise reduction device according to the present invention for the purpose of achieving the object is characterized by including: a pair of objects formed of a porous material; a band member for attaching the objects to the inner surface of a tire at two positions spaced at substantially equal intervals in the tire circumferential direction; and locking members formed of a thermoplastic resin. The noise reduction device also has the following characteristics. The band member is formed of a thermoplastic resin. Each object is disposed at a predetermined position in the tire circumferential direction, between the band member and the corresponding locking member. The locking members are bonded to the band member through the objects by thermal fusion.

In addition, a method of manufacturing a noise reduction device according to the present invention for the purpose of achieving the object is a method of manufacturing a noise reduction device including a pair of objects formed of a porous material and a band member for attaching the objects to the inner surface of a tire at two positions spaced at substantially equal intervals in the tire circumferential direction. The method is characterized by including: forming the band member of a thermoplastic resin; disposing each object at a predetermined position in the tire circumferential direction, between the band member and locking members formed of a thermoplastic resin, and bonding the locking members to the band member through each object by thermal fusion.

In the present invention, while the band member is formed of a thermoplastic resin, objects for changing the cross-sectional area of a cavity portion of a pneumatic tire is disposed between the band member and the locking members formed of a thermoplastic resin, and the locking members are bonded to the band member through the objects by thermal fusion. Accordingly, even when the objects are formed of a thermosetting resin, such as polyurethane foam, it is possible to firmly fix the objects to the band member. The fixation by thermal fusion bonding does not cause a reduction in adhesive force due to decomposition reaction, unlike the fixation by using an adhesive agent or an adhesive tape. For this reason, it is possible to maintain the bonding state of the objects formed of a porous material favorably over a long period of time. In addition, the processing by thermal fusion bonding can be completed for a short period of time, as compared with the processing by using an adhesive agent. As a result, the processing time of the noise reduction device can be reduced.

It is preferable that a constituent material of the band member and a constituent material of the locking members be the same thermoplastic resin, and for example, be polypropylene. Meanwhile, it is preferable that the porous material of the objects be polyurethane foam. In other words, since the polyurethane foam exhibits a favorable noise absorbing characteristic, the polyurethane foam is preferable as the constituent material of the objects.

In the noise reduction device according to the present invention, each locking member may have a plate shape, or may have a cylindrical shape with a bottom. The locking members having a cylindrical shape with a bottom have an advantage that the locking members are less likely to damage the objects formed of a porous material. In addition, through holes may be formed in advance in each object at positions where the object is locked by the locking members. In this case, it is preferable that the objects are held in the state of being compressed by the locking members when the locking members are bonded to the band member via the through holes by thermal fusion. This makes it possible to suppress the movements of the objects formed of a porous material. Moreover, an edge portion of each object may be retained by a fastener formed of a thermoplastic resin, and then the fastener may be bonded to the band member by thermal fusion. This makes it possible to suppress the movements of the edge portions of the objects formed of a porous material, and to thus prevent the portions from being destructed.

In addition, in the noise reduction device according to the present invention, it is preferable that the width of each locking member be 90 to 300% of the width of the band member, that the width of a thermal-fusion-bonding portion of each locking member and the band member be made narrower than the width of the band member, and that non-fusion-bonding portions, each having a width equivalent to 5 to 20% of the width of the band member, be left on both sides of the thermal-fusion-bonding portion. This makes it possible to firmly fix the objects to the band member while securing the durability of the band member. Moreover, it is preferable that the thermal-fusion-bonding portions of the locking members and the band member are arranged at intervals in the tire circumferential direction, and the relation between the interval H and the width W of each object is 0.2W≦H≦4W. This makes it possible to secure the preferable durability by minimum processing.

In the method of manufacturing a noise reduction device according to the present invention, it is preferable that an ultrasonic welder be used for bonding each locking member and the band member to each other by thermal fusion. In the case of using such an ultrasonic welder, it is possible to locally heat each locking member and the band member. As a result, an excellent balance between the processability and the durability can be achieved. The ultrasonic welder is effective particularly when the constituent material of the band member and the constituent material of the locking members are polypropylene. In addition, by employing, as an oscillating horn for the ultrasonic welder, one having chamfered end portions of a tip in the width direction thereof, it is possible to suppress an occurrence of a whitening phenomenon in the locking members, and thus to further improve the durability.

According to the present invention, provided is a pneumatic tire including the noise reduction device in a cavity portion thereof. In such a pneumatic tire, the cross-sectional area of the cavity portion is changed in accordance with a position in the tire circumferential direction due to the existence of the pair of objects. Accordingly, the cavity resonance frequency is changed as the tire rotates, so that time during which air resonates at the same single frequency is reduced. As a result, it is possible to effectively reduce the road noise associated with the cavity resonance. Moreover, since the durability of the objects formed of a porous material is excellent, the noise reduction effect can be maintained over a long period of time.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective cross-sectional view showing a pneumatic tire according to an embodiment of the present invention.

FIG. 2 is a perspective view showing a noise reduction device according to the embodiment of the present invention.

FIG. 3 show an example of a method of thermal fusion bonding between a locking member and a band member, and each of FIGS. 3( a) to 3(c) is a cross-sectional view showing a step of the method.

FIG. 4 is a perspective view showing an example of an oscillating horn for an ultrasonic welder.

FIG. 5 is a perspective view showing another example of the oscillating horn for the ultrasonic welder.

FIG. 6 is a perspective view showing another example of the oscillating horn for the ultrasonic welder.

FIG. 7 is a front view of the oscillating horn shown in FIG. 6.

FIG. 8 is a cross-sectional view showing a structure in which thermal fusion bonding is performed on the locking member.

FIG. 9 is a cross-sectional view showing an object to which a notch portion is provided in advance.

FIG. 10 is a cross-sectional view showing the object to which a cut is provided in advance.

FIG. 11 is a plan view showing a state where the noise reduction device is expanded on the plane.

FIG. 12 is a plan view showing a detail of the noise reduction device.

FIG. 13 is a cross-sectional view showing a state where a modified example of the noise reduction device is expanded on the plane.

FIG. 14 is a cross-sectional view showing a state where a modified example of the noise reduction device is expanded on the plane.

FIG. 15 is a plan view showing a state where a modified example of the noise reduction device is expanded on the plane.

FIG. 16 is a perspective view showing a modified example of the noise reduction device.

FIG. 17 show a noise reduction device using cylindrical locking members. FIG. 17( a) is a perspective view showing a state of the noise reduction device before thermal fusion bonding while FIG. 17( b) is a perspective view showing a state of the noise reduction device after the thermal fusion bonding.

FIG. 18 show an example of a method of thermal fusion bonding between the cylindrical locking member and the band member, and each of FIGS. 18( a) and 18(b) is a cross-sectional view showing a step of the method.

FIG. 19 show a noise reduction device using frusto-conical cylindrical locking members. FIG. 19( a) is a perspective view showing a state of the noise reduction device before thermal fusion bonding while FIG. 19( b) is a perspective view showing a state of the noise reduction device after the thermal fusion bonding.

FIG. 20 show an example of a method of thermal fusion bonding between the frusto-conical cylindrical locking member and the band member. Each of FIGS. 20( a) and 20(b) is a cross-sectional view showing a step of the method.

FIG. 21 is a perspective view showing a noise reduction device using a fastener for retaining the edge portion of the object formed of a porous material.

FIG. 22 is a perspective view showing a noise reduction device using a fastener for retaining the edge portion of the object formed of the porous material.

FIG. 23 is a perspective view showing a noise reduction device using a fastener for retaining the edge portion of the object formed of the porous material.

FIG. 24 is a perspective view showing a noise reduction device using a fastener for retaining the edge portion of the object formed of the porous material.

FIG. 25 is a side view showing a noise reduction device using a fastener for retaining the edge portion of the object formed of the porous material.

FIG. 26 show an example of a method of thermal fusion bonding between the fastener and the band member, and each of FIGS. 26( a) and 26(b) is a side view showing a step of the method.

FIG. 27 show another example of the method of thermal fusion bonding between the fastener and the band member, and each of FIGS. 27( a) and 27(b) is a side view showing a step of the method.

BEST MODES FOR CARRYING OUT THE INVENTION

Hereinafter, descriptions will be given in detail of a configuration of the present invention with reference to the accompanying drawings. FIG. 1 shows a pneumatic tire according to an embodiment of the present invention. FIG. 2 shows a noise reduction device according to the embodiment of the present invention. In FIG. 1, a pneumatic tire is provided with a tread portion 1, a pair of left and right bead portions 2, and side wall portions 3. Each of the side wall portions 3 connects the tread portion 1 and a corresponding one of the bead portions 2 to each other. In addition, a ring-shaped noise reduction device 4 shown in FIG. 2 is attached to the inner surface of the tread portion 1.

The noise reduction device 4 is provided with a pair of objects 5 and 5 formed of a porous material, and a band member 6 for attaching these objects 5 and 5 to the inner surface of the tire at two positions spaced at substantially equal intervals in the tire circumferential direction. The pair of objects 5 and 5 are arranged in positions facing each other over the rotational axis of the tire for maintaining the weight balance, and concurrently for sufficiently fulfilling the noise reduction effect associated with a change in the cross-sectional area of a cavity portion. Each object 5 may include internal cells so as to have a noise reduction characteristic associated with the porous structure by itself. As the porous material for the objects 5, polyurethane foam may be used. On the other hand, the band member 6 is shaped into a ring in a manner of extending continuously in the tire circumferential direction. The band member 6 holds the objects 5 on the inner surface of the tire with the elastic restoring force thereof. The noise reduction device 4 configured as described above is attachable to, and detachable from, general pneumatic tires, and is thus easy to be attached and detached.

In the noise reduction device 4, thermal fusion bonding is employed as means for fixing the objects 5 and the band member 6. For enabling the thermal fusion bonding, the band member 6 is formed of a thermoplastic resin. In addition, plate-shaped locking members 7 (locking plates or locking chips) formed of a thermoplastic resin are used. Specifically, the pair of objects 5 and 5 are arranged at predetermined positions in the tire circumferential direction between the band member 6 and the locking members 7 formed of the thermoplastic resin. Then, the locking members 7 are bonded to the band member 6 through each of the objects 5 by thermal fusion. As the constituent material of the band member 6 and the constituent material of the locking members 7, the same thermoplastic resin, for example, polypropylene may be used.

FIGS. 3( a) to 3(c) show an example of a method of thermal fusion bonding between the locking member and the band member. Firstly, as shown in FIG. 3( a), the object 5 is disposed between the band member 6 and the locking member 7. Thereafter, as shown in FIG. 3( b), an oscillating horn 11 for an ultrasonic welder is pressed against the locking member 7, so that the locking member 7 is bent. Then, the tip portion where the locking member 7 is bent is locally heated. In this manner, as shown in FIG. 3( c), the locking member 7 and the band member 6 are bonded to each other through the object 5 by thermal fusion, so that a thermal-fusion-bonding portion 8 is formed.

In the thermal fusion bonding using the ultrasonic welder, the shape of the oscillating horn 11 is not particularly limited. For example, the oscillating horns 11 having shapes as shown in FIGS. 4 to 6 may be employed. In FIG. 4, the oscillating horn 11 has a tip processed into a sharp linear shape. In FIG. 5, the oscillating horn 11 has a tip processed into a long and thin rectangular surface. In FIG. 6, the oscillating horn 11 has a tip processed into a long and thin rectangular surface, and further has chamfered portions 11 a formed in both end portions of the tip in the width direction thereof. FIG. 7 is a side view of the oscillating horn shown in FIG. 6. It is preferable that the radius of curvature of each chamfered portion 11 a be not less than 2 mm. The chamfering of both end portions, in the width direction, of the tip of the oscillating horn 11, makes it possible to suppress an occurrence of a whitening phenomenon in the locking member 7 due to the pressing of the oscillating horn 11.

In the thermal fusion bonding using the ultrasonic welder, the dimensions and the shape of the locking member 7 are not particularly limited. The shape of the locking member 7 may be, for example, a quadrangle. In this case, it is preferable to round the corners of the quadrangle. This makes it possible to reduce the damaging of the object 5 by the locking member 7. In addition, as shown in FIG. 8, in a state where the locking member 7 is bonded to the band member 6 by thermal fusion, it is preferable that the clearance C between each end portion of the locking member 7 and the upper surface of the object 5 satisfy 0.5 mm≦C≦8.0 mm. When the clearance C is less than 0.5 mm, the object 5 is likely to be damaged by the locking member 7. On the other hand, even when the clearance C is more than 8.0 mm, a better result cannot be obtained than that of a case where the clearance C is 8.0 mm. In addition, a notch portion 5 a as shown in FIG. 9 or a cut 5 b as shown in FIG. 9 may be provided to the object 5 in a portion where the locking member 7 is disposed.

In the above-described noise reduction device 4, while the band member 6 is formed of the thermoplastic resin, the objects 5 providing a change in the cross-sectional area of the cavity portion of the pneumatic tire are disposed between the band member 6 and the locking members 7, and then the locking members 7 are bonded to the band member 6 through the objects 5 by thermal fusion. Accordingly, even when the objects 5 are formed of a thermosetting resin, such as polyurethane foam, it is possible to firmly fix the objects 5 to the band member 6. The fixation by thermal fusion bonding does not cause a reduction in adhesive force due to decomposition reaction, unlike the fixation by using an adhesive agent or an adhesive tape. For this reason, it is possible to improve the adhesion of the objects 5 formed of the porous material. In addition, since the processing by thermal fusion bonding can be completed for a shorter time than the processing by using an adhesive agent, it is possible to reduce time taken for processing the noise reduction device 4.

Moreover, the pneumatic tire provided with the noise reduction device 4 in the cavity portion makes it possible to obtain an excellent noise reduction effect with the objects 5. Furthermore, it is possible to maintain the noise reduction effect over a long period of time.

FIG. 11 shows a state where the noise reduction device is expanded on the plane. As shown in FIG. 11, the thermal-fusion-bonding portions 8 of the locking members 7 and the band member 6 may be arranged at intervals (pitches) in the tire circumferential direction, and the relation between the interval H and the width W of the object 5 may be 0.2W≦H≦4W. When the relation is 0.2W>H, the workability at the time of thermal fusion bonding is deteriorated. When the relation is H>4W, the bonding state of the objects 5 to the band member 6 is unstable. In addition, the thermal-fusion-bonding portion 8 may be provided to each object 5 in 3 or more positions, or preferably in 5 or more positions. This makes it possible to stably hold the objects 5, which are disposed non-continuously in the tire circumferential direction. In each object 5, the thermal-fusion-bonding portions 8 may be arranged at equal intervals.

FIG. 12 shows a detail of the noise reduction device. As shown in FIG. 12, the width Wt of each locking member 7 may be set at 90 to 300% of the width Wb of the band member 6. The width Wm of each of the thermal-fusion-bonding portions 8 of the locking members 7 and the band member 6 may be made narrower than the width Wb of the band member 6, so that non-fusion-bonding portions are left on both sides of each thermal-fusion-bonding portion 8 in the width direction thereof. The width Wx of each non-fusion-bonding portion may be set at 5 to 20% of the width Wb of the band member 6. When the width Wt of each locking member 7 is less than 90% of the width Wb of the band member 6, the fixation of each object 5 is insufficient. When the width Wt is more than 300% thereof, the operation of thermal fusion bonding is difficult. In addition, when the width Wx of each non-bonding portion is less than 5% of the width Wb of the band member 6, the strength of the band member 6 is insufficient. When the width Wx is more than 20% thereof, the fixation of each object 5 is insufficient. Incidentally, the thickness of each locking member 7 may be in a range from 20 to 150% of the thickness of the band member.

Each of FIGS. 13 and 14 shows a state where a modified example of the noise reduction device is expanded on the plane. In FIG. 13, the locking member 7 extends continuously along the band member 6, and is fixed to the band member 6 with a plurality of the thermal-fusion-bonding portions 8. In FIG. 14, although the locking member 7 extends continuously along the band member 6 as in the same manner as that in FIG. 13, the locking member 7 has some extra length for allowance.

FIG. 15 shows a state where a modified example of the noise reduction device is expanded on the plane. Specifically, the thermal-fusion-bonding portions 8 are formed in 5 portions, in the tire circumferential direction, of each object 5 in FIG. 11, the thermal-fusion-bonding portions 8 are formed in only 3 portions in the tire circumferential direction, in FIG. 15.

FIG. 16 shows another modified example of the noise reduction device. Incidentally, in FIG. 16, the description of each object formed of the porous material is omitted. In FIG. 16, the plate-shaped locking member 7 is bonded to the band member 6 by thermal fusion but the thermal-fusion-bonding portion is formed obliquely with respect to the longitudinal direction of the band member 6. In this case, since the thermal-fusion-bonding portion 8 is made longer, the durability can be improved.

FIGS. 17( a) and 17(b) show another modified example of the noise reduction device. In FIGS. 17( a) and 17(b), the object 5 is disposed between the band member 6 and locking members 17 formed of a thermoplastic resin, and each locking member 17 is bonded to the band member 6 through the object 5 by thermal fusion. Each locking member 17 has a cylindrical shape with a bottom, and is provided with a flange on the open end side thereof. On the other hand, through holes 5 c are formed in advance in the object 5 at positions where the object 5 is to be locked by the locking members 17. Each through hole 5 c has a shape into which the shape of the locking member 17 fits. In the case of using the cylindrical locking members 17 each having no sharp edge portion or corner, the object 5 formed of the porous material is less likely to be damaged.

FIGS. 18( a) and 18(b) show an example of a method of thermal fusion bonding between the cylindrical locking member and the band member. Firstly, as shown in FIG. 18( a), the cylindrical locking member 17 is inserted into the through hole 5 c of the object 5, and then an oscillating horn 21 for an ultrasonic welder is pressed against the bottom portion of the locking member 17, so that the bottom portion is locally heated. The pressing surface of the oscillating horn 21 is circular. In this manner, as shown in FIG. 18( b), the locking member 17 is bonded to the band member 6 through the object 5 by thermal fusion. At this time, it is preferable that the object 5 be held in the state of being compressed by the locking member 17. In this case, the ratio (Hb/Ha) of the height Hb of the compressed portion of the object 5 to the height Ha of the object in a normal state may preferably be not more than 0.8, and more preferably be not more than 0.5.

FIGS. 19( a) and 19(b) show another modified example of the noise reduction device. In FIGS. 19( a) and 19(b), the object 5 is disposed between the band member 6 and locking members 27 formed of a thermoplastic resin, and the locking members 27 are bonded to the band member 6 through the object 5 by thermal fusion. Each locking member 27 has a frusto-conical cylindrical shape with a bottom. In each locking member 27, the diameter at the open end side is larger than the diameter at the bottom side. On the other hand, through holes 5 d, each of which is slightly narrower than the size of each locking member 27, is formed in advance in the object 5 at positions where the object 5 is locked by the locking members 27. In the case of using the frusto-conical cylindrical locking members 27 each having no sharp edge portion or corner, the object 5 formed of the porous material is less likely to be damaged.

FIGS. 20( a) and 20(b) show an example of a method of thermal fusion bonding between the frusto-conical cylindrical locking member and the band member. Firstly, as shown in FIG. 20( a), the frusto-conical cylindrical locking member 27 is inserted into the through hole 5 d of the object 5, then the oscillating horn 21 for the ultrasonic welder is pressed against the bottom portion of the locking member 27, and the bottom portion is locally heated. In this manner, as shown in FIG. 20( b), the locking member 27 is bonded to the band member 6 through the object 5 by thermal fusion. At this time, it is preferable that the object 5 be held in the state of being compressed by the locking member 27. The ratio (Hb/Ha) of the height Hb of the compressed portion of the object 5 to the height Ha of the object in a normal state may also preferably be not more than 0.8, and more preferably be not more than 0.5.

Each of FIGS. 21 to 25 shows another modified example of the noise reduction device. In each of FIGS. 21 to 24, the edge portion of the object 5 is forced down by a fastener 31 formed of a thermoplastic resin, and the fastener 31 is bonded to the band member 6 by thermal fusion. The shape of the fastener 31 is not particularly limited, and may be one of various shapes as shown in the figures. The edge portions of the object 5 tend to move during the rolling of the tire, but suppressing the movement of the portions with the fastener 31 makes it possible to prevent the object 5 from being destructed. Moreover, as shown in FIG. 25, it is preferable that a gap is provided between the fastener 31 and the object 5. This makes it possible to avoid interference between the fastener 31 and the object 5.

FIGS. 26( a) and 26(b) show an example of a method of thermal fusion bonding between the fastener and the band member. As shown in FIG. 26( a), as the fastener 31, one having an angle larger than the inclination angle of the side wall of the object 5 may be used. In this case, as shown in FIG. 26( b), when being bonded to the band member 6 by thermal fusion, the fastener 31 holds the object 5 in a compressed state.

FIGS. 27( a) and 27(b) show another example of a method of thermal fusion bonding between the fastener and the band member. As shown in FIG. 27( a), as the fastener 31, a simple plate-shaped one may be used. In this case, as shown in FIG. 27( b), when being bonded to the band member 6 by thermal fusion, the fastener 31 holds the object 5 in a compressed state while being elastically deformed.

Descriptions have been given above in detail of the preferred embodiments of the present invention. It should be understood that various modifications, alternations and substitutions can be made on the embodiments as long as not departing from the spirit and the scope of the present invention, which are defined by the scope of the appended claims.

EXAMPLES

Noise reduction devices of Conventional Example, as well as Examples 1 and 2 were prepared. The noise reduction device of Conventional Example was prepared as follows. A pair of objects formed of band-shaped urethane foam (a length of 480 mm by a width of 150 mm by a thickness of 20 mm) were fixed to a band member formed of polypropylene (a width of 20 mm by a thickness of 2 mm by a length equal to that of the inner periphery of the tire) at positions spaced at equal intervals in the tire circumferential direction by using an adhesive agent. Then the band member was formed into a circular shape. On the other hand, the noise reduction device of Example 1 was prepared as follows. A pair of objects formed of band-shaped urethane foam (a length of 480 mm by a width of 150 mm by a thickness of 20 mm) were disposed on a band member formed of polypropylene (a width of 20 mm by a thickness of 2 mm by a length equal to that of the inner periphery of the tire) at positions spaced at equal intervals in the tire circumferential direction. Then, by using an ultrasonic welder, plate-shaped locking members formed of polypropylene were bonded to the band member through the objects formed of urethane foam by thermal fusion. The noise reduction device of Example 2 was prepared in the same manner as that of Example 1, except that frusto-conical cylindrical locking members were used. In each of the noise reduction devices of Examples 1 and 2, thermal-fusion-bonding portions are provided to each object at 3 positions in the tire circumferential direction.

Each of the noise reduction devices of Conventional Example as well as Examples 1 and 2 was installed in a pneumatic tire having a tire size of 215/55R16, and was then caused to run by using a drum testing machine under the conditions of an internal pressure of 150 kPa and a speed of 80 km/h, so that the distance for which the tire ran until the object was detached was measured. The results of the tests are shown in Table 1. The evaluation results are indicated by indices where the evaluation result of Conventional Example is taken as 100. The larger the index is, the more favorable the durability of the tire is.

TABLE 1 Conventional Example Example 1 Example 2 Means for Fixing Objects Adhesive Thermal Thermal Providing Change in Agent Fusion Fusion Cross-sectional Area Bonding Bonding Running Distance (Index) 100 134 165

As is clear from Table 1, the noise reduction devices of Examples 1 and 2 were significantly improved in the durability as compared with that of Conventional Example. 

What is claimed is:
 1. A pneumatic tire comprising a noise reduction device in a cavity portion thereof, the noise reduction device comprising: a pair of objects formed of a porous material; a band member formed of a thermoplastic resin for attaching the objects to the inner surface of a tire at two positions spaced at substantially equal intervals in the tire circumferential direction; and locking members formed of a thermoplastic resin; wherein each object is disposed at a predetermined position in the tire circumferential direction, between the band member and the locking members, the locking members are bonded to the band member through the objects by thermal fusion, and a constituent material of the band member and a constituent material of the locking members are same thermoplastic resin.
 2. The pneumatic tire according to claim 1, wherein the constituent material of the band member and the constituent material of the locking members are polypropylene.
 3. The pneumatic tire according to claim 2, wherein the porous material of the objects is polyurethane foam.
 4. The pneumatic tire according to claim 2, wherein each locking member has a plate shape.
 5. The pneumatic tire according to claim 2, wherein each locking member has a cylindrical shape with a bottom.
 6. The pneumatic tire according to claim 5, wherein through holes are formed in each object at positions where the object is locked by the locking members.
 7. The pneumatic tire according to claim 6, wherein the objects are held in the state of being compressed by the locking members when the locking members are bonded to the band member via the through holes by thermal fusion.
 8. The pneumatic tire according to claim 2, wherein an edge portion of each object is retained by a fastener formed of a thermoplastic resin, and then the fastener is bonded to the band member by thermal fusion.
 9. The pneumatic tire according to claim 2, wherein the width of each locking member is 90 to 300% of the width of the band member, the width of a thermal-fusion-bonding portion where each locking member is bonded to the band member by thermal fusion is made narrower than the width of the band member, and non-fusion-bonding portions, each having a width equivalent to 5 to 20% of the width of the band member, are left on both sides of the thermal-fusion-bonding portion.
 10. The pneumatic tire according to claim 9, wherein the thermal-fusion-bonding portions of the locking members and the band member are arranged at intervals in the tire circumferential direction, and the relation between the interval H and the width W of each object is 0.2W≦H≦4W.
 11. The pneumatic tire according to claim 1, wherein the porous material of the objects is polyurethane foam.
 12. The pneumatic tire according to claim 1, wherein each locking member has a plate shape.
 13. The pneumatic tire according to claim 1, wherein each locking member has a cylindrical shape with a bottom.
 14. The pneumatic tire according to claim 13, wherein through holes are formed in each object at positions where the object is locked by the locking members.
 15. The pneumatic tire according to claim 14, wherein the objects are held in the state of being compressed by the locking members when the locking members are bonded to the band member via the through holes by thermal fusion.
 16. The pneumatic tire according to claim 1, wherein an edge portion of each object is retained by a fastener formed of a thermoplastic resin, and then the fastener is bonded to the band member by thermal fusion.
 17. The pneumatic tire according to claim 1, wherein the width of each locking member is 90 to 300% of the width of the band member, the width of a thermal-fusion-bonding portion where each locking member is bonded to the band member by thermal fusion is made narrower than the width of the band member, and non-fusion-bonding portions, each having a width equivalent to 5 to 20% of the width of the band member, are left on both sides of the thermal-fusion-bonding portion.
 18. The pneumatic tire according to claim 17, wherein the thermal-fusion-bonding portions of the locking members and the band member are arranged at intervals in the tire circumferential direction, and the relation between the interval H and the width W of each object is 0.2W≦H≦4W. 